.TH ANTLR 1 "September 1995" "ANTLR" "PCCTS Manual Pages"
.SH NAME
antlr \- ANother Tool for Language Recognition
.SH SYNTAX
.LP
\fBantlr\fR [\fIoptions\fR] \fIgrammar_files\fR
.SH DESCRIPTION
.PP
\fIAntlr\fP converts an extended form of context-free grammar into a
set of C functions which directly implement an efficient form of
deterministic recursive-descent LL(k) parser.  Context-free grammars
may be augmented with predicates to allow semantics to influence
parsing; this allows a form of context-sensitive parsing.  Selective
backtracking is also available to handle non-LL(k) and even
non-LALR(k) constructs.  \fIAntlr\fP also produces a definition of a
lexer which can be automatically converted into C code for a DFA-based
lexer by \fIdlg\fR.  Hence, \fIantlr\fR serves a function much like
that of \fIyacc\fR, however, it is notably more flexible and is more
integrated with a lexer generator (\fIantlr\fR directly generates
\fIdlg\fR code, whereas \fIyacc\fR and \fIlex\fR are given independent
descriptions).  Unlike \fIyacc\fR which accepts LALR(1) grammars,
\fIantlr\fR accepts LL(k) grammars in an extended BNF notation \(em
which eliminates the need for precedence rules.
.PP
Like \fIyacc\fR grammars, \fIantlr\fR grammars can use
automatically-maintained symbol attribute values referenced as dollar
variables.  Further, because \fIantlr\fR generates top-down parsers,
arbitrary values may be inherited from parent rules (passed like
function parameters).  \fIAntlr\fP also has a mechanism for creating
and manipulating abstract-syntax-trees.
.PP
There are various other niceties in \fIantlr\fR, including the ability to
spread one grammar over multiple files or even multiple grammars in a single
file, the ability to generate a version of the grammar with actions stripped
out (for documentation purposes), and lots more.
.SH OPTIONS
.IP "\fB-ck \fIn\fR"
Use up to \fIn\fR symbols of lookahead when using compressed (linear
approximation) lookahead.  This type of lookahead is very cheap to
compute and is attempted before full LL(k) lookahead, which is of
exponential complexity in the worst case.  In general, the compressed
lookahead can be much deeper (e.g, \f(CW-ck 10\fP) than the full
lookahead (which usually must be less than 4).
.IP \fB-CC\fP
Generate C++ output from both ANTLR and DLG.
.IP \fB-cr\fP
Generate a cross-reference for all rules.  For each rule, print a list
of all other rules that reference it.
.IP \fB-e1\fP
Ambiguities/errors shown in low detail (default).
.IP \fB-e2\fP
Ambiguities/errors shown in more detail.
.IP \fB-e3\fP
Ambiguities/errors shown in excruciating detail.
.IP "\fB-fe\fP file"
Rename \fBerr.c\fP to file.
.IP "\fB-fh\fP file"
Rename \fBstdpccts.h\fP header (turns on \fB-gh\fP) to file.
.IP "\fB-fl\fP file"
Rename lexical output, \fBparser.dlg\fP, to file.
.IP "\fB-fm\fP file"
Rename file with lexical mode definitions, \fBmode.h\fP, to file.
.IP "\fB-fr\fP file"
Rename file which remaps globally visible symbols, \fBremap.h\fP, to file.
.IP "\fB-ft\fP file"
Rename \fBtokens.h\fP to file.
.IP \fB-ga\fP
Generate ANSI-compatible code (default case).  This has not been
rigorously tested to be ANSI XJ11 C compliant, but it is close.  The
normal output of \fIantlr\fP is currently compilable under both K&R,
ANSI C, and C++\(emthis option does nothing because \fIantlr\fP
generates a bunch of #ifdef's to do the right thing depending on the
language.
.IP \fB-gc\fP
Indicates that \fIantlr\fP should generate no C code, i.e., only
perform analysis on the grammar.
.IP \fB-gd\fP
C code is inserted in each of the \fIantlr\fR generated parsing functions to
provide for user-defined handling of a detailed parse trace.  The inserted
code consists of calls to the user-supplied macros or functions called
\fBzzTRACEIN\fR and \fBzzTRACEOUT\fP.  The only argument is a
\fIchar *\fR pointing to a C-style string which is the grammar rule
recognized by the current parsing function.  If no definition is given
for the trace functions, upon rule entry and exit, a message will be
printed indicating that a particular rule as been entered or exited.
.IP \fB-ge\fP
Generate an error class for each non-terminal.
.IP \fB-gh\fP
Generate \fBstdpccts.h\fP for non-ANTLR-generated files to include.
This file contains all defines needed to describe the type of parser
generated by \fIantlr\fP (e.g. how much lookahead is used and whether
or not trees are constructed) and contains the \fBheader\fP action
specified by the user.
.IP \fB-gk\fP
Generate parsers that delay lookahead fetches until needed.  Without
this option, \fIantlr\fP generates parsers which always have \fIk\fP
tokens of lookahead available.
.IP \fB-gl\fP
Generate line info about grammar actions in C parser of the form
\fB#\ \fIline\fP\ "\fIfile\fP"\fR which makes error messages from
the C/C++ compiler make more sense as they will \*Qpoint\*U into the
grammar file not the resulting C file.  Debugging is easier as well,
because you will step through the grammar not C file.
.IP \fB-gs\fR
Do not generate sets for token expression lists; instead generate a
\fB||\fP-separated sequence of \fBLA(1)==\fItoken_number\fR.  The
default is to generate sets.
.IP \fB-gt\fP
Generate code for Abstract-Syntax Trees.
.IP \fB-gx\fP
Do not create the lexical analyzer files (dlg-related).  This option
should be given when the user wishes to provide a customized lexical
analyzer.  It may also be used in \fImake\fR scripts to cause only the
parser to be rebuilt when a change not affecting the lexical structure
is made to the input grammars.
.IP "\fB-k \fIn\fR"
Set k of LL(k) to \fIn\fR; i.e. set tokens of look-ahead (default==1).
.IP "\fB-o\fP dir
Directory where output files should go (default=".").  This is very
nice for keeping the source directory clear of ANTLR and DLG spawn.
.IP \fB-p\fP
The complete grammar, collected from all input grammar files and
stripped of all comments and embedded actions, is listed to
\fBstdout\fP.  This is intended to aid in viewing the entire grammar
as a whole and to eliminate the need to keep actions concisely stated
so that the grammar is easier to read.  Hence, it is preferable to
embed even complex actions directly in the grammar, rather than to
call them as subroutines, since the subroutine call overhead will be
saved.
.IP \fB-pa\fP
This option is the same as \fB-p\fP except that the output is
annotated with the first sets determined from grammar analysis.
.IP "\fB-prc on\fR
Turn on the computation and hoisting of predicate context.
.IP "\fB-prc off\fR
Turn off the computation and hoisting of predicate context.  This
option makes 1.10 behave like the 1.06 release with option \fB-pr\fR
on.  Context computation is off by default.
.IP "\fB-rl \fIn\fR
Limit the maximum number of tree nodes used by grammar analysis to
\fIn\fP.  Occasionally, \fIantlr\fP is unable to analyze a grammar
submitted by the user.  This rare situation can only occur when the
grammar is large and the amount of lookahead is greater than one.  A
nonlinear analysis algorithm is used by PCCTS to handle the general
case of LL(k) parsing.  The average complexity of analysis, however, is
near linear due to some fancy footwork in the implementation which
reduces the number of calls to the full LL(k) algorithm.  An error
message will be displayed, if this limit is reached, which indicates
the grammar construct being analyzed when \fIantlr\fP hit a
non-linearity.  Use this option if \fIantlr\fP seems to go out to
lunch and your disk start thrashing; try \fIn\fP=10000 to start.  Once
the offending construct has been identified, try to remove the
ambiguity that \fIantlr\fP was trying to overcome with large lookahead
analysis.  The introduction of (...)? backtracking blocks eliminates
some of these problems\ \(em \fIantlr\fP does not analyze alternatives
that begin with (...)? (it simply backtracks, if necessary, at run
time).
.IP \fB-w1\fR
Set low warning level.  Do not warn if semantic predicates and/or
(...)? blocks are assumed to cover ambiguous alternatives.
.IP \fB-w2\fR
Ambiguous parsing decisions yield warnings even if semantic predicates
or (...)? blocks are used.  Warn if predicate context computed and
semantic predicates incompletely disambiguate alternative productions.
.IP \fB-\fR
Read grammar from standard input and generate \fBstdin.c\fP as the
parser file.
.SH "SPECIAL CONSIDERATIONS"
.PP
\fIAntlr\fP works...  we think.  There is no implicit guarantee of
anything.  We reserve no \fBlegal\fP rights to the software known as
the Purdue Compiler Construction Tool Set (PCCTS) \(em PCCTS is in the
public domain.  An individual or company may do whatever they wish
with source code distributed with PCCTS or the code generated by
PCCTS, including the incorporation of PCCTS, or its output, into
commercial software.  We encourage users to develop software with
PCCTS.  However, we do ask that credit is given to us for developing
PCCTS.  By "credit", we mean that if you incorporate our source code
into one of your programs (commercial product, research project, or
otherwise) that you acknowledge this fact somewhere in the
documentation, research report, etc...  If you like PCCTS and have
developed a nice tool with the output, please mention that you
developed it using PCCTS.  As long as these guidelines are followed,
we expect to continue enhancing this system and expect to make other
tools available as they are completed.
.SH FILES
.IP *.c
output C parser.
.IP *.cpp
output C++ parser when C++ mode is used.
.IP \fBparser.dlg\fP
output \fIdlg\fR lexical analyzer.
.IP \fBerr.c\fP
token string array, error sets and error support routines.  Not used in
C++ mode.
.IP \fBremap.h\fP
file that redefines all globally visible parser symbols.  The use of
the #parser directive creates this file.  Not used in
C++ mode.
.IP \fBstdpccts.h\fP
list of definitions needed by C files, not generated by PCCTS, that
reference PCCTS objects.  This is not generated by default.  Not used in
C++ mode.
.IP \fBtokens.h\fP
output \fI#defines\fR for tokens used and function prototypes for
functions generated for rules.
.SH "SEE ALSO"
.LP
dlg(1), pccts(1)
